Vintage Synth Repair

thanks a lot! so i already went out and got two 15 pf caps to replace
the 30 pf cap (you can do that right?) 

do you know if they'll be any negative side effects of adjusting that
trim?

thanks for the advice, i'll let you know how it goes! i think i better
do the test points next...

-johnny


--- In vintagesynthrepair@yahoogroups.com, Malte Rogacki <gacki@...>
wrote:
>
> > i didn't even realize it but "c2" the capacitor hooked to pin 1 and 8
> > of the op amp is totally broken. classic newbie move i guess. fix one
> > problem and cause two more. so now i'm looking in the user manual and
> > i don't see a value for that part in the parts list of board C-1. do
> > you happen to know what the value of that component is?
> 
> http://en.wikipedia.org/wiki/Opamp#Class_A_gain_stage
> 
> If you're using a modern internally compensated opamp this capacitor
might
> not even be needed; however if you're using a LM301 like in the
original it
> is 30pF as indicated on the schematic. Because this is a "standard
value"
> as described in the wikipedia link it is probably not in the parts list.
> 
> I don't think this should cause this behaviour, though.
> 
> There are a few other points but you might first want to check out the
> voltage on pin 3 and 4 of the filter module. Pin 3 is the output of the
> opamp (and hence the various modulation sources), pin 4 is the cutoff
> slider.
> There's also a trimmer (T3) that is used to fine-tune the cutoff
frequency;
> if that one is completely out of range it might affect the frequency as
> well.
> 
> I'm working on a Odyssey Mk3 at the moment myself.
> 
> 
> -- 
> Malte Rogacki gacki@...
>
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> "Don't forget to TURN ON THE SYNTHESIZER. Often this is the reason
why you
>  get no sound out of it." (ARP 2600 Owner's Manual)
>
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>